It is known that Fenton's reagent comprising hydrogen peroxide and a ferrous ion source is a strong oxidation reagent. There have been many studies investigating the mechanism of the oxidative reaction of organic compounds by this Fenton's reagent. In particular, studies by Norman, R.O.C. et al. (J. Chem. Soc., B, 1099, 1970) and Walling, C., et al; (J. Am. Chem. Soc. 95, 948, 1973) indicated that the oxidative reactions of organic compounds by Fenton's reagent was based on the free radical reaction of .cndot.OH which was produced by the reaction of ferrous ion with hydrogen peroxide.
U.S. Pat. No. 4,102,312 discloses the use of ultraviolet light to irradiate hydrogen peroxide to enhance the oxidation ability of hydrogen peroxide. Jefcoate, C.R.E., et al (J. Chem Soc., B., 1013, 1969) have also compared the oxidizing characteristics of a reagent system using UV irradiation and H.sub.2 O.sub.2 and a treatment system using Fenton's reagent in the hydroxylation of benzene derivatives.
There are a number of studies where the photocatalytic effects of 3d transition metal ions on the photolysis of hydrogen peroxide have been investigated. Sedlak, P., et al (Collection Czechoslovak Chem. Commun., 52, 2451, 1987) measured the quantum yields of H.sub.2 O.sub.2 photolysis and photoinitiated hydroxylation of 2-hydroxybenzoic acid in the presence of 3d transition metals and observed marked photocatalytic effects only for Cu.sup.2+ in H.sub.2 O.sub.2 photolysis and for Fe.sup.3+ in photoinitiated hydroxylation of 2-hydroxybenzoic acid. Further studies on the photocatalytic effects of Cu.sup.2+ by the same investigators indicated that the high quantum yields of hydrogen peroxide are due to thermal decomposition of hydrogen peroxide catalyzed by photochemically generated copper ions in oxidation states which are catalytically active (Lunak, S., et al, Collection Czechoslovak Chem. Commun., 51 973, 1986).
Xia, Guoshou et al (China Environmental Science, 8(3), June 1988) studied the effects of various reaction conditions in the treatment of nitrobenzene and nitrotoluene using hydrogen peroxide and Fe.sup.2+ and Cu.sup.2+ in the presence of UV irradiation or sunlight. The UV light source used in the study was a low pressure mercury arc with helix shape and 20 W power. This light source was essentially a monochromatic light source with output at 254 nm. The maximum elimination efficiency was obtained when both Fe.sup.2+ and Cu.sup.2+ were used as the catalyst and hydrogen peroxide was added in batches.
The processes suggested in the literature suffer from a number of disadvantages. Many of the organic contaminants most commonly found in effluents and groundwaters, such as ethers, aromatics, chlorinated aromatics etc, would not be efficiently removed using these processes since high concentrations of iron ions would be needed which results in a treated water product requiring further treatment steps to remove the iron before it may be discharged into the environment. The processes suggested in the literature also do not recognize the importance of H.sub.2 O.sub.2 absorbance and the photochemical conversion of the transition metals, particularly when operating the process on a commercial scale.